A pre-programmed universal forward-looking calendar can predict sunrise and sunset times in a known way by latitude or time zone. That calendar can include a preset number of programs to control the actual on/off cycle of a streetlight. However, the clock must be phased at installation to local conditions or time, and maintained in correct time, or must be a simple on/off or fixed-time-on-after-sunset design. Those approaches are not ideal across the seasons.
There have been various solutions for controlling street lamps, starting with central controls, often via vacuum tube photocells of the 1920s, and progressing through now widely used individual fixture mounted light sensing controls. Current controls generally use a light sensitive resistor (e.g., a Cadmium sulfide cell) or a photodiode, with solid state processing or timing systems. Such timing systems include various programmable clocks and photocells in combination.
As energy conservation concerns have become more pronounced, the timing systems have become more important. There are several prior art designs which use a combination of a photocell and a pre-programmed duration timer. A timer or clock arrangement can be set or programmed in the field, a long known approach. It also can come preprogrammed with a specific “on” time, in hours, after sensing sundown.
The latter devices will need various versions with differing “light on” times in hours to stock and inventory, sometimes multiplied by specific voltage ratings or switches and taps to set these things at installation. They are also dependent each time (i.e., daily) on photocells or other external inputs to set the initial time of operation. They are presently in worldwide use.
Field programmable individual per light timing units (i.e., clock based) bring up the problem of how to program them easily in a harsh environment (e.g., a utility truck) and the lineman's time and external devices needed to do that programming. This problem, and cost, prevents wide adoption of field programmable devices as of 2011, except for simple “hours on after dark” energy saving designs. For instance, U.S. Pat. No. 6,011,755 to Mulhad describes an electric meter-like enclosure with many keys (e.g., for input), which is not cost effective or practical for individual streetlights. These presently use small simple controls which snap onto the top of the light fixture via a twist-lock socket, ideally with no user inputs.
Further, any streetlight control dependent on photodiode light levels for any function, including phasing of internal clocks to determine sunup and sundown, is subject to problems from shadows, tall buildings, trees, or other spurious lighting such as flood lights. These problems can occur in tunnels, under bridges, parking garages or in narrow city streets. They make operation inherently variable, and sometimes impossible. However, the photodiode approach is useful in open country.
Systems dependent strictly by time still are used widely. Programming needs to be done, whether mechanical or by often complex computer I/O or networked systems, both to set the local time and to set up a calendar program based on local solar events. “Time only” operation, by just a clock, requires a tracking of daily sunset and sunup times. Such tracking requires either an automatic or manual seasonal adjustment, or periodic resetting, or a stored geographically dependent calendar. This means concepts involving precision time (e.g., as disseminated by WWV) still do not address local sunup and sundown in the installed time zone without manual or automatic intervention.
WWV is the call sign of the National Institute of Standards' (“NIST's”) shortwave radio station located in Fort Collins, Colo. WWV's main function is the continuous dissemination of official U.S. Government time signals.
Daily tracking of sunset and sundown for any local phasing purpose reverts to the problems of photocells described above, which may or may not be tolerable, depending on view or exposure. However, integrating these events over many days can be a valuable approach and is described herein to predict the next day's sunset, and then storing that information digitally.
Individual control of lamps is widely preferred, due to immunity to total failure of many lamps at one time, and cost issues of signal wires or networks. These calendar and clock functions can be implemented, for example, by computers and programming in microprocessors. However, cost effectiveness of this approach at each lamp is an issue, due to the need to “set it up”. Software corruption by transients can happen at any time over a 10-20 year life of the device, giving further pause to this approach due to reliability concerns. Battery backup over a 15-year life also can be a difficult and troublesome prerequisite.
All of the above approaches may be described as suboptimal for universal use as a low-cost and simple, reliable stand-alone and independent outside area lighting or sign control.
Accordingly, is a primary object of the present invention to provide a method and apparatus for synchronizing the on and off time for streetlights by sensing and analyzing local conditions without human intervention.
It is another primary object to provide a control system for turning streetlights off, when such lighting is not needed, to conserve energy.